1. Field of the Invention
The invention relates to an engine control apparatus and engine control method, and more particularly, to an engine control apparatus and engine control method which obtains a target engine torque based on an accelerator operation amount when controlling the driving force of a vehicle, and performs engine control so that the engine torque becomes equal to the target engine torque.
2. Description of the Related Art
A structure is known which obtains a target engine torque based on an accelerator operation amount when controlling the driving force of a vehicle, and performs engine control so that the engine output torque becomes equal to the target engine torque. In this kind of engine control, the engine torque characteristics are obtained beforehand under a predetermined environmental condition, and the engine torque is adjusted based on the target engine torque and the engine torque characteristics obtained beforehand.
However, when the environmental condition changes from the predetermined environmental condition, the actual engine torque characteristics also change such that when the engine torque is adjusted using the engine torque characteristics that were obtained under the predetermined environmental condition, the driving force that is achieved does not accurately reflect the driving force desired by the driver.
Regarding this point, Japanese Patent Application Publication No. JP-A-9-112329 proposes obtaining the maximum engine torque and the minimum engine torque that are actually able to be generated based on an environmental condition such as atmospheric pressure or intake air temperature, and then obtaining the target engine torque by interpolating it between the obtained maximum engine torque and the minimum engine torque.
More specifically, an interpolation block is applied with the target engine torque as a ratio (MPED) between the minimum engine torque and the maximum engine torque. The interpolation block obtains a target engine torque (MFAR) by interpolating it between the maximum engine torque (MMAX) and the minimum engine torque (MMIN) that are actually able to be generated, according to that ratio (MPED) (i.e., MFAR=MPED×(MMAX−MMIN)+MMIN). As a result, a target engine torque that corresponds to an accelerator operation by the driver can be set which reflects a change in the environment such as the atmospheric pressure or the intake air temperature or the like.
When there is a change in the environment, the maximum engine torque characteristic changes with respect to a change in engine speed in a manner unlike the maximum engine torque characteristic obtained in advance under the predetermined environmental condition. Therefore, as with the technology described in Japanese Patent Application Publication No. JP-A-9-112329, when the target engine torque is obtained, the engine torque characteristics to be used in obtaining the target engine torque become distorted with respect to the engine torque characteristics that were obtained beforehand under the predetermined environmental condition.
On the other hand, the control constants and the like that are used to control various devices for adjusting engine torque are applied based on the engine torque characteristics under the predetermined environmental condition. Therefore, the correlation between the engine torque characteristics used in obtaining the target engine torque and the engine torque characteristics behind controlling the devices for adjusting the engine torque is lost. As a result, accuracy in controlling the engine torque deteriorates, resulting in deterioration in drivability.